@Christian-Dirk-Helmut-Karpinski-Lime-Unicorn#146042 @TimothyAlexander#146061 Next to the answer already provided (putting the amount in the url), the alternative option is to use the bunqme-tab endpoint in the API to create a payment request and then redirect the user to the generated URL:
https://doc.bunq.com/#/bunqme-tab
This is a lot more complex of course than the URL method, but the advantage is that the amount cannot be changed by the payer, and that the payment can be tracked more easily through the API as well.